Liquid crystal temperature sensor and materials

ABSTRACT

Liquid crystal temperature indicating compositions, preferably absent cholesteric liquid crystal material, and the containing of such compositions in volumes formed in a containment medium (29) that tends to distort the liquid crystal structure (36) when the temperature thereof is below a transition or clearing point temperature (FIG. 4). The containment medium (29) is water resistant, e.g. insoluble in water, and preferably has heat and optical stability, e.g., does not brown or otherwise discolor, at relatively high temperatures, e.g. above 100° C. Plural liquid crystal materials having different transition temperatures may be mixed to form a liquid crystal material having a transition temperature intermediate those of the ingredients (FIG. 11). In such distorted or curvilinearly aligned mesomorphic phase, the index of refraction of the liquid crystal is different, preferably greater, than that of the containment medium; therefore, incident light (11) will be scattered (21), preferably isotropically, and such scattered light can be used as a temperature identifier (FIG. 1). However, above a transition temperature, the liquid crystal material changes to an isotropic phase (30), which is substantially optically transparent, on the one hand; and the liquid crystal is so selected such that in the isotropic phase it has an index of refraction substantially matching that of the containment medium (29) (FIG. 5). Incident light (11) is transmitted (24) by the isotropic liquid crystal (23) and, accordingly, provides another temperature identifier (FIG. 3). The scattering liquid crystal material will appear visually brighter than the transmitting liquid crystal material, especially when illumination is provided by light from a source (7) independent of ambient light (FIG. 1). Moreover, dye can be used to color the scattered light.

This is a divisional of co-pending application Ser. No. 06/829,652 filedon Jan. 22, 1986, now U.S. Pat. No. 4,884,877, which is acontinuation-in-part of copending U.S. patent application Ser. No.612,906, filed May 22, 1984, now abandoned, the entire disclosure ofwhich hereby is incorporated by reference.

TECHNICAL FIELD

The present invention relates generally, as indicated, to liquid crystaldevices for sensing temperature, to compositions of liquid crystalmaterial and of containment media and to methods of making and usingsuch liquid crystal material and media. The invention relates totemperature sensing and to thermometric uses of liquid crystal.

CROSS-REFERENCE TO RELATED PATENTS AND APPLICATIONS

U.S. Pat. No. 4,435,047, issued Mar. 6, 1984.

U.S. patent applications Ser. No. 477,138 and Ser. No. 477,242, bothfiled Mar. 21, 1983, now U.S. Pat. Nos. 4,606,611 and 4,616,903,respectively.

U.S. patent applications Ser. No. 480,461 and Ser. No. 480,466, bothfiled Mar. 30, 1983, now U.S. Pat. Nos. 4,662,720 and 4,596,445,respectively.

U.S. patent application Ser. No. 585,883, filed Mar. 2, 1984, now U.S.Pat. No. 4,707,080.

The inventor of the instant application also is the inventor in theabove patent and applications. The disclosures of such patent andapplications hereby are incorporated in their entireties by referencethereto.

BACKGROUND

Liquid crystal materials have been used in the past for temperaturesensing purposes. An example of one liquid crystal temperature sensor isdisclosed in U.S. Pat. No. 4,140,016. In that patent the temperaturesensor employs nematic liquid crystal with an optically activeingredient to cause the nematic liquid crystal to twist so that lightordinarily would be reflected by the liquid crystal material when thetemperature thereof is below a so-called transition point temperature orclearing point temperature (the same being used interchangeably herein),whereby the liquid crystal material is in a mesomorphic phase. However,on reaching and exceeding the transition or clearing point temperature,the liquid crystal enters an isotropic phase and becomes substantiallyoptically transparent. The transition temperature can be selected as afunction of the ingredients and proportions thereof which are employedto formulate the liquid crystal material. One disadvantage encounteredwith prior liquid crystal temperature sensors has been the difficulty inreading the same due to inadequate lighting.

Other prior liquid crystal temperature sensor devices have usedcholesteric liquid crystal material which ordinarily undergoes a changein apparent color as a function of temperature. One disadvantagefrequently encountered with cholesteric temperature sensing devices isthe relatively slow reversing, indeed sometimes the non-reversiblenature, of the material, for cholesteric liquid crystal frequently isknown to have a relatively long relaxation and/or memory characteristic.Another disadvantage with cholesteric liquid crystal temperature sensorsis the relatively low temperature maximum of, say, on the order of 100°C. to which the same would be operatively responsive.

The encapsulation or otherwise containment of liquid crystal material,particularly operationally nematic liquid crystal material, in volumesformed in a containment, encapsulating or support medium, is disclosedin the above referenced patent and applications. Moreover, the liquidcrystal material and containment medium therein disclosed cooperate suchthat in the absence of a prescribed input the containment medium tendsto distort the natural liquid crystal structure to a so-calledcurvilinear or distorted alignment. The extraordinary index ofrefraction of the liquid crystal material, which occurs in the absenceof such input, is greater than the index of refraction of thecontainment medium; and, therefore, incident light impinging on thecontained liquid crystal material will tend to be scattered preferablysubstantially isotropically. However, in the presence of a prescribedinput, such as an electric field, the liquid crystal structure tends toalign with respect to such input; the ordinary index of refraction ofthe liquid crystal material preferably is fairly closely matched to thatof the containment medium; and, accordingly, the amount of scattering(or absorption) of the incident light is reduced. Also disclosed inapplication Ser. No. 477,138, is a reflector arrangement which reflectsa fairly large amount of the isotropically scattered light back to theliquid crystal material for further isotropic scattering thereby. Suchreflection increases or enhances the effective brightness of thescattering contained liquid crystal material. The principle of totalinternal reflection can be relied on to achieve such reflectioncharacteristic and, thus, the desired enhanced brightening.

A possible disadvantage of various media that have been used toencapsulate or to contain liquid crystal material is that such media mayencounter substantial and/or relatively rapid discoloring, e.g.browning, when subjected to relatively high temperatures. Anotherpossible disadvantage is that at relatively high temperatures the liquidcrystal may dissolve into the medium.

Representative objects of the invention are to provide a liquid crystaltemperature sensor that has a wide range of temperature responses, iscapable of having high temperature response in particular, rapidlyresponds to temperature, has a sharp transition between mesomorphic andisotropic phases, is relatively promptly reversible, has the ability tobe formulated to provide relatively widely different transitiontemperatures, and is relatively long lasting; and as to the containmentmedium, in particular, which contains plural volumes of liquid crystal,does not encounter discoloring or at least rapid discoloring of thecontainment medium and does not find the liquid crystal dissolvingtherein. Other objects are to provide improved liquid crystal materials,containment media, methods and techniques for sensing and indicatingtemperature as well as methods and techniques for formulating suchliquid crystal material and devices employing the same.

BRIEF SUMMARY OF THE INVENTION

Briefly, the present invention relates to temperature indicatingcompositions, devices and methods. Several important aspects of theinvention include a discovery of how to use liquid crystal materials fortemperature sensing without requiring a cholesteric liquid crystaladmixture, of improved liquid crystal materials and methods of makingand using same, of the ability to mix liquid crystal materials to obtaina composition having a transition temperature that is a function of thetransition points of the ingredients and the proportional quantities ofthe ingredients, of improved non-discoloring or slow discoloringcontainment media for holding volumes of liquid crystal material fortemperature sensing, and of the containing of such liquid crystalcompositions in volumes formed in a containment medium that tends todistort the liquid crystal structure when the temperature thereof isbelow a transition or clearing point temperature.

While the liquid crystal material is in such distorted or curvilinearlyaligned mesomorphic phase, the index of refraction thereof is different,preferably is greater, than the index of refraction of the containmentmedium. However, if the temperature of the liquid crystal materialexceeds a transition temperature, the liquid crystal material changes toan isotropic phase, which is substantially optically transparent, on theone hand, and the liquid crystal, then, is so selected as to have anindex of refraction that substantially matches the index of refractionof the containment medium. Therefore, when the liquid crystal is in themesomorphic, distorted and curvilinearly aligned phase, incident lightwill be scattered, preferably isotropically, and such scattered lightcan be used as an identifier that the temperature of the liquid crystalmaterial is below the transition temperature. On the other hand, whenthe liquid crystal material is in the isotropic phase, incident light istransmitted thereby and, accordingly, the same provides anotheridentifier that the temperature of the liquid crystal material is at orabove the transition temperature. The scattering liquid crystal materialwill appear visually brighter than the transmitting liquid crystalmaterial. Moreover, dye can be added, preferably to the containmentmedium, to color the scattered light. Also, to maximize longevity and tooptimize operation a containment medium that does not dissolve theliquid crystal and that is slow or non-browning in response to elevatedtemperature is employed.

The terms "transition temperature", "transition point", "clearingtemperature", and "clearing point" as used throughout the specificationand claims of this application mean the point or temperature at whichthe liquid crystal composition or compound passes from the mesomorphicphase to the form of an isotropic liquid or isotropic phase.

The present invention preferably employs nematic or smectic liquidcrystal material alone or in combination with each other and possiblywith cholesteric liquid crystal material. However, the liquid crystalmaterial should primarily be operationally nematic or operationallysmectic, which means that such material operates in at least certainways like nematic or smectic liquid crystal material. Importantconsiderations in such operability include, in particular, the abilityof the liquid crystal structure or the orientation thereof to beresponsive, and in large part determined, by boundary effect, i.e. theaffect of the boundary of the liquid crystal material with, for example,the internal wall of a containment medium within which the liquidcrystal material is contained in volumes or capsule-like spaces. Suchvolumes may be fluidically isolated from each other or may befluidically connected to one or more similar volumes. The liquid crystalmaterial also should have at least two different phases, one amesomorphic phase and the other an isotropic phase, the latter usuallyoccurring at and above a specific transition temperature. As usedherein, moreover, the terms encapsulating, encapsulated, contained,containment, etc., medium, means a medium, such as an encapsulating orcontaining medium, for containing such liquid crystal material thereinin the aforementioned volumes.

The terms distorted alignment or curvilinearly aligned, etc., refer tothe distorting of the natural structure of the liquid crystal materialin the mesomorphic or anisotropic phase by the walls of the volumesformed in the containment medium. Such natural structure may be, andpreferably is, generally linear. Such distorted or curvilinearly alignedstructure may be a forced orientation of the liquid crystal structure toa parallel relation to the volume wall (such volume walls being curved,e.g. for a generally spherical volume, say of capsule-likeconfiguration, would result in a general curving of the liquid crystalstructure) or in an alternate embodiment to a generally normal relationto the volume wall. Further description of curvilinear or distortedalignment is presented in the above-referenced patent and applications.

According to one aspect of the invention, then, liquid crystal materialfor scattering or transmitting light incident thereon as a function oftemperature of the liquid crystal is contained in volumes formed in acontainment medium which tends to distort the liquid crystal structurewhen the temperature thereof is below the transition temperature. Due tothe unmatched indices of refraction of the liquid crystal material andcontainment medium, then, incident light will be substantiallyisotropically scattered. However, at temperatures at and above thetransition temperature, due to the clarity of the liquid crystalmaterial and the matching of the indices of refraction of the liquidcrystal material and containment medium, incident light will betransmitted and generally not scattered. Therefore, and optical resultthat is a function of temperature is able to be accomplished by nematicor smectic liquid crystal or a combination thereof without the need fora temperature sensitive color changing cholesteric liquid crystalmaterial or, if desired, with a cholesteric liquid crystal ingredient.

According to another aspect of the invention, light scattered by suchmesomorphic or anisotropic phase liquid crystal material in such atemperature sensing device is reflected back to the scattering liquidcrystal material to brighten the visual appearance thereof. Moreover,such reflection may be provided, according to still another aspect ofthe invention, by total internal reflection principles. Such brightappearance would be in contrast to a relatively darker appearance of theliquid crystal material that is above transition temperature in clear,light transmitting isotropic phase.

According to even another aspect of the invention, a liquid crystaltemperature sensing and indicating device includes an illuminating lightsource for illuminating the liquid crystal material during temperaturesensing operation. An important advantage of this arrangement is theability to examine temperatures in dark or other relatively difficult toaccess.

Still another aspect relates to an improved liquid crystal material,especially for temperature sensing, and methods for making same.

According to further aspects, liquid crystal materials are combined incompositions to achieve a composition with a desired transition point,indeed in some cases below ordinary room ambient temperature; andelimination or reduction of detrimental discoloring of the containmentmedium and/or absorbing therein of liquid crystal material in responseto relatively high temperatures.

An important advantage of the invention is the versatility oftemperature responses, and, in particular, the ability to sense or torespond to and to indicate temperatures at relatively elevated levelscompared to the lower temperature restriction of cholesteric liquidcrystal materials. Such advantage is accomplished, for example, due tothe higher temperature capabilities of the liquid crystal material(s) ormixed employed, the reliance on isotropic point and not exclusively oncolor change, and the matched index of refraction characteristics formaximizing clarity or distinguishability of the output.

According to one embodiment of the invention a temperature sensor andindicator includes liquid crystal for scattering or transmitting lightincident thereon as a function of temperature of the liquid crystal, acontainment medium for containing plural volumes of the liquid crystaland distorting the natural structure of the liquid crystal when in themesomorphic phase, and a support for supporting the volumes of liquidcrystal in the containment medium for sensing temperature, the liquidcrystal having a mesomorphic or anisotropic phase at temperatures belowa transition temperature and an isotropic phase at temperatures at andabove such transition temperature.

According to another embodiment of the invention a temperature sensorincludes liquid crystal material having an isotropic phase at and abovea transition temperature and a mesomorphic or anisotropic phase belowsuch transition temperature, a containment medium for containing theliquid crystal material in curvilinear alignment configuration at leastat temperatures below such transition temperature, the liquid crystalmaterial, when in such mesomorphic or anisotropic phase, having an indexof refraction different from the containment medium to scatter lightincident thereon and the liquid crystal material, when in such isotropicphase, having an index of refraction substantially matched to that ofthe containment medium to reduce such scattering of light incidentthereon.

According to an additional embodiment of the invention a composition ofmatter includes, a) from 0 to 100 mole percent of a first liquid crystalmaterial, and b) from 0 to 100 mole percent of a second liquid crystalmaterial; the composition of matter having a mesomorphic or anisotropicphase at temperatures below a transition temperature and an isotropicphase at and above such transition temperature, and the transitiontemperature being in the range of about 26° C. to about 75° C. (Notethat when 100 percent of one liquid crystal material is used, the otherliquid crystal material is not used in the composition; therefore, thetransition temperature for a composition using 100 percent of one liquidcrystal material would be that of such used liquid crystal material.

According to a further embodiment of the invention, a composition ofmatter includes:

a) from 0 to 100 mole percent of a first liquid crystal material, and

b) from 0 to 100 mole percent of a second liquid crystal material,

(the total amount of material should add to 100 percent)

the composition of matter having a mesomorphic or anisotropic phase attemperatures below a transition temperature and an isotropic phase atand above such transition temperature, and each of the first and secondliquid crystal material being selected from a respective one of thefollowing compositions,

    ______________________________________                                        i)   PePMeOB                    39.6%,                                             PPPOB                      26.6%                                              4-Ethylphenyl-propylbenzoate                                                                             33.8%                                         ii)  PPMeOB                     60%                                                PPPOB                      40%                                           iii) A mixture of about 52% of                                                     (1) a mix of                                                                  PPMeOB 60% and PPPOB 40%   82%                                                (2) Bis(4-butoxybenzoyl)-2-methylhydroquinone                                                            18%                                                and about 48% of                                                              (1) CnPPeB                 33%                                                (2) CnPHepB                50%                                                (3) Bis(4-pentylbenzoyl)-2-methylhydroquinone                                                            17%                                           ______________________________________                                    

Several abbreviations used herein are, as follows:

PePPOB means 4-n-pentylphenyl-4-n-pentoxybenzoate

PePMeOB means 4-n-pentylphenyl-4-n-methoxybenzoate

CnPPeB means 4-cyanophenyl-pentylbenzoate

CnPHepB means 4-cyanophenyl-heptylbenzoate

PPPOB means 4-n-pentylphenyl-4-n-pentyloxybenzoate

PPMeOB means 4-n-pentylphenyl-4-n-methoxybenzoate

Also, unless otherwise noted herein percentages of liquid crystalmaterials are mole percents.

According to yet another embodiment of the invention a composition ofmatter includes a) from about 30% to less than about 100%Bis-butoxylmethylhydroquinone, and b) from more than about 0% to about70% Bis-pentylmethylhydroquinone. Such composition may have a transitiontemperature up to about 205° C.

According to yet an additional embodiment of the invention, atemperature sensor includes liquid crystal for scattering ortransmitting light incident thereon as a function of temperature of theliquid crystal, and containment medium for containing plural volumes ofthe liquid crystal, the containment medium being formed of a materialthat undergoes no or slow discoloring in response to relatively hightemperature and that does not dissolve the liquid crystal at relativelyhigh temperatures.

According to yet a further embodiment of the invention, a temperaturesensor includes liquid crystal for scattering or transmitting lightincident thereon as a function of temperature of the liquid crystal, andcontainment medium for containing plural volumes of the liquid crystal,the liquid crystal comprising at least one of nematic liquid crystalmaterial and smectic liquid crystal material in the absence of acholesteric liquid crystal material admixed therewith.

The foregoing and additional objects, advantages, and features of theinvention will become more apparent as the following descriptionproceeds and with appropriate observation of the drawings.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter described in the specificationand particularly pointed out in the claims, the following descriptionand the annexed drawings setting forth in detail a certain illustrativeembodiment of the invention, this being indicative, however, of but oneof the various ways in which the principles of the invention may beemployed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

FIG. 1 is a side elevation view of a liquid crystal temperature sensorin accordance with the present invention operative to scatter light;

FIG. 2 is a top plan view of the liquid crystal temperature sensor ofFIG. 1 looking generally in the direction of the arrows 2--2 of FIG. 1;

FIG. 3 is a side elevation view of the liquid crystal temperature sensorwherein the liquid crystal material is in the isotropic phase;

FIG. 4 is a schematic section view illustration of a capsule or volumeof a containment medium containing liquid crystal material in themesomorphic of curvilinearly aligned phase;

FIG. 5 is a schematic section view illustration of a capsule or volumeof a containment medium containing liquid crystal materiual in theisotropic phase;

FIG. 6 is a view similar to FIG. 4 in which the liquid crystal structureis aligned generally normal to the capsule or volume wall;

FIG. 7 is an illustration of another alternate embodiment of a volume ofencapsualted liquid crystal material and a containment medium with anadditive for enhancing the return of the liquid crystal material fromisotropic phase to mesomorphic, curvilinearly aligned phase;

FIGS. 8 and 9 are, respectively, fragmentary schematic section views ofliquid crystal material, respectively, in mesomorphic, curvilinearlyaligned phase and in isotropic phase, as used to scatter or to transmitlight in connection with the liquid crystal temperature sensor of FIGS.1-3;

FIG. 10 is a schematic section view illustration of a capsule or volumeof a containment medium containing liquid crystal material in themesomorphic of curvilinearly aligned phase similar to the illustrationof FIG. 4, but with the addition of dye to the containment medium; and

FIG. 11 is a graph depicting the relationships between compositions ofrespective mixtures of liquid crystal material in accordance with theinvention and transition temperature thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring in detail to the drawings, wherein like reference numeralsdesignate like parts in the several figures and initially to FIGS. 1, 2and 3, a liquid crystal temperature sensor in accordance with thepresent invention is generally indicated at 1. The fundamentalcomponents of the liquid crystal temperature sensor 1 include at leastone, in the preferred illustrated embodiment four, temperature sensitiveliquid crystal segments 2-5, a support 6 for supporting those segments,and preferably a light source 7 for directing incident light to theliquid crystal segments. A combination handle and housing 10 enclosesthe light source 7, provides a mounting for the support 6, andfacilitates manual manipulation of the liquid crystal temperature sensor1.

As will be described in greater detail below, each liquid crystalsegment 2-5 is formed of liquid crystal material in a containment mediumthat tends to distort the natural liquid crystal structure to acurvilinearly aligned formed when in the mesomorphic phase; and eachsegment 2-5 has a unique transition temperature at and above which theliquid crystal therein changes to isotropic phase. In the mesomorphic,curvilinearly aligned phase, each segment tends to scatter lightincident thereon, and in the isotropic phase, the segment(s) tend(s) totransmit light incident thereon. The light source 7 provides a source ofillumination for the liquid crystal segments 2-5. Such illumination isprovided along an optical path represented at 11 generally in parallelto the support 6, as is seen in FIG. 1. A window 12 in the housing 10provides an exit for light from the source 7 to travel along the lightpath 11.

The light source 7 is connected in an electrical circuit 13, whichincludes a battery 14 for energizing the light source and a switch 15,such as a push button switch that may be selectively closed to completethe circuit 13 for energizing the light source 7 to emit light. Thehousing 10 may include a track 16 along which the support 6 may slide towithdraw the support and the liquid crystal segments 2-5 into thehousing for protected storage. For that purpose, using thumb pressure orforce while the housing 10 is held in a hand, the top of the switch 15may be urged to the right, relative to the illustration in FIGS. 1-3, toslide the support 6 also to the right and into the housing. During suchsliding the switch/button 15 slides along a slot 17 provided in the topof the housing. If desired, the switch 15 may be separate from a deviceemployed to effect the aforementioned sliding motion.

Preferably the support 6 is formed of a good thermally conductivematerial, such as, for example, steel coated with aluminum or nickel.The thermal conduction properties of the support 6 facilitate conductingheat to the liquid crystal segments 2-5. The support 6 may be generallyreflective; although in the preferred embodiment and best mode of theinvention, part of the top surface of the support 6 is black or in anyevent made to be of minimal reflectivity to avoid reflecting lighttransmitted along path 11, while those portions of the support 6directly beneath the liquid crystal segments 2-5 preferably areoptically reflective to facilitate and to enhance brightening of theliquid crystal segments when the same are operative to scatter light.

To use the liquid crystal temperature sensor 1 in accordance with thepresent invention, the switch 15 is slid to the left to expose thesupport 6 and liquid crystal segments 2-5 from the housing 10. Theswitch 15 is closed, e.g. by pressing same, to energize the circuit 13causing the light source 7 to direct light along the light path 11toward the liquid crystal segments 2-5. The support 6 is placed intoengagement with a surface, device, environment, etc., the temperature ofwhich is to be sensed. Those liquid crystal segments 2-5, if any, thatremain in the mesomorphic, curvilinearly aligned phase, will tend toscatter light received along the light path 11, such scattering beingrepresented at 20 in FIG. 1 for visual observation by a user looking inthe direction 21 toward the top surface 22 of the respective liquidcrystal segments. Those scattering liquid crystal segments will appearrelatively bright on visual inspection, e.g. from the top. However,those liquid crystal segments 2-5, if any, which are raised to atemperature that is at or above the transition temperature, will becomeclear and no longer will scatter light. In fact, what will occur is thatlight directed along the light path 11 from the source 7 will tend to betransmitted through such liquid crystal segment(s), if any, escaping outthrough the end 23 of the liquid crystal segment(s) along a continuation24 of the light path 11. Accordingly, such segments of liquid crystalmaterial that are in the isotropic phase will appear relatively darkcompared to those which are in the mesomorphic, scattering phase.

Turning now to FIG. 4, one of the many volumes 29 of contained liquidcrystal material in accordance with the present invention is shownschematically. Such volume 29 is represented as a single capsule.However, as is mentioned above, it will be appreciated that the volumesmay be fluidically interconnected with one or more of the same in agiven liquid crystal segment 2-5, for example. The volume or capsule 29includes liquid crystal material 30, a number of the molecules orstructural components 31 thereof being shown by the various dashed linesin the figure contained within a capsule 32. At the interior wall 33 ofthe capsule 32 defining the boundary of the volume of liquid crystal 30the liquid crystal molecules or structural components 31 are distortedfrom normal straight line configuration, which is the natural structureof nematic and smectic liquid crystal material, to a curvilinearlyaligned configuration or structure that is generally parallel to thewall 33. In particular, those molecules or structural components 31which are most proximate the wall 33, i.e. at the boundary therewith,for example those represented at 34, are close to parallel, if notcompletely parallel, to the wall 33, and those molecules or structuralcomponents represented at 35 or remote from the wall 33 still tend tohave a curvilinearly aligned structure due to the influence of theliquid crystal proximate the wall 33. Additionally, due to thedistortion of the liquid crystal structure in the capsule 32, there mayoccur a discontinuity 36 in the structural alignment of the liquidcrystal to allow the liquid crystal to assume a lowest free energy statein the capsule when otherwise undisturbed.

The capsule 32 preferably is formed of a binding medium, containmentmedium, support medium, etc., that preferably is generally opticallytransparent (or may be dyed with an appropriate color dye, if desired).Such medium has an idex of refraction. To achieve the desired scatteringof light when the liquid crystal material 30 is in the mesomorphic oranisotropic phase curvilinearly aligned, as is shown, for example, inFIG. 4, the index of refraction of such liquid crystal material isgreater than, and preferably much greater than, the index of refractionof the medium. As a result of such distortion of the liquid crystalstructure and the difference between such indices of refraction, light,such as that traveling along light path 11 (FIG. 1) incident on a liquidcrystal segment including a plurality of volumes 29 of liquid crystalmaterial 30 will tend to be scattered substantially isotropically. Suchscattered light may be seen by looking in the viewing direction 21,whereby the respective liquid crystal segment(s) 2(-5, i.e. those belowthe respective transition temperature) will appear relatively bright toan observer.

When the liquid crystal material 30 in the volume 29 is raised to thetransition temperature or above the transition temperature, such liquidcrystal material becomes an isotropic material, which is schematicallyrepresented in FIG. 5. Such isotropic material is represented in FIG. 5by a plurality of dots; such dots are intended to represent a change inthe liquid crystal structure from the curvilinearly aligned structure tothe isotropic phase. Importantly, to maximize light transmission throughthe liquid crystal capsule or volume 29 when the liquid crystal materialis in the isotropic phase, the index of refraction of such liquidcrystal material in the isotropic phase preferably is matched to besubstantially the same, if not identical, to the index of refraction ofthe containment medium 32. Such proximity or identity of those indicesof refraction will permit maximum undistorted, unrefracted, andunscattered transmission of light through the respective liquid crystalsegment(s) 2 (-5), for example, in the manner illustrated in FIG. 3described above. In this event since minimum light is scattered forviewing in the viewing direction 21, the respective liquid crystalsegment(s) 2 (-5) in the isotropic phase will appear relatively darkcompared to the scattering liquid crystal material still in themesomorphic phase, for example.

Briefly referring to FIG. 6, the volume 29' of encapsulated or containedliquid crystal material 30' in accordance with another embodiment of theinvention is illustrated. The primary difference between the volume 29'of FIG. 6 and the volume 29 of FIG. 4 is that in FIG. 6 the liquidcrystal molecules or structural components 31' are aligned generally ata non-parallel angle with respect to the capsule 32' wall 33'. In fact,the liquid crystal structure in FIG. 6 tends to be aligned in what maybe referred to as normal or perpindicular alignment with the wall 33' atthe boundary or interface with such wall, and the other liquid crystalin the volume 29' more remote from that boundary also tends to beinfluenced by the boundary condition and alignment so as to retaincharacteristics of normal alignment, as is seen in the drawing.Operation of the embodiment illustrated in FIG. 6 would be similar tooperation according to the embodiments illustrated in FIGS. 4 and 5, aswas described in greater detail above. Specifically, light scatteringwill occur when the liquid crystal structure is curvilinearly aligned inthe form, for example, illustrated in FIG. 6; and a reduction inscattering, and preferably transmission of light, will occur when theliquid crystal material is in the isotropic phase at and above thetransition temperature.

An important advantage of the present invention over the prior colorchanging cholesteric liquid crystal temperature sensor devices is theability of the nematic and/or smectic liquid crystal that may be used inthe present invention to withstand temperatures up to approximately 205°C. Ordinarily cholesteric liquid crystal will not functionsatisfactorily at temperatures above 100° C. Therefore, the presentinvention has particularly high temperature operational capability. Inthe above-mentioned U.S. Pat. No. 4,140,016, an inert additive isrequired to achieve desired twist in the nematic liquid crystal. Suchadditive is described, for example, as a cholesteric material.Therefore, the device of such patent would not necessarily be expectedto operate at the higher temperatures at which the present inventionwould be operable.

However, according to the embodiment illustrated in FIG. 7, for example,which may be construed as a relatively lower temperature capabilityembodiment of the present invention, a volume 29" of contained orencapsulated liquid crystal material, for example similar to thatdescribed above with reference to the volume 29 illustrated in FIG. 4,also includes an additive 39. The additive 39 may be, for example, achiral additive which tends to expedite and to enhance distortion--nottwisting--of the liquid crystal material 30" in the capsule 32".

Turning now to FIGS. 8 and 9, an enlarged view of a preferred embodimentand best mode of the present invention in the form of a liquid crystalsegment 2, respectively in the mesomorphic, curvilinearly aligned,anisotropic phase and isotropic phase is illustrated. The segment 2 isformed of a plurality of volumes 29, for example, of liquid crystalmaterial 30 and a containment medium 32. The containment medium may be,for example, polyvinyl alcohol, and preferably is a combination thereofwith carboxylic acid-containing polymers such as described in moredetail below which medium also may form protective layers 40, 41 aboveand below the so-called encapsulated liquid crystal layer 42. Thecontainment medium prevents contamination of the liquid crystal materialin the volumes 29. Such layers 40, 41 may be reduced in height and/ormay be eliminated, especially if the protective function thereof is notrequired. The support 6 has a polished or optically reflective coating43 beneath the area where the segment 2 is formed to reflect lightinpinging on such surface.

Incident light 44 along light path 11 from the light source 7 (FIG. 1)impinges on the liquid crystal layer 42 as well as on the protectivelayers 40, 41. Since the protective layers 40, 41 generally areoptically transparent, the light 44 impinging thereon will tend to betransmitted through the same and out through the left-hand end thereof,relative to the illustration of FIG. 8. However, light impinging orincident on the mesomorphic liquid crystal layer 42 will tend to bescattered preferably substantially isotropically thereby. An example ofone light ray or beam scattered out through the top surface 45 of thesegment 2 for viewing from the viewing direction 21 is illustrated at50. Light scattered or reflected toward the surface 45 and fallingwithin a relatively narrow cone angle with respect to a normal to thesurface, such as the ray 50, which is perpendicular to the surface 45,will tend to be transmitted out through such surface for viewing.However, another scattered light ray 51 outside such cone angle andincident on the interface of the surface 45 with the externalenvironment, such as air (represented at 52), will be totally internallyreflected at such interface as ray 53 back toward the liquid crystallayer 42 for further illuminating and effectively brightening the same.Such total internal reflection will occur when the index of refractionof the layer 40, such as polyvinyl alcohol or a combination thereof withother polymeric material (described in greater detail below), exceedsthe index of refraction of the external medium 52, such as air, when theangle of the light ray 51 is outside the predetermined cone angle, aswould be apparent to those having ordinary skill in the art and as isdescribed, for example, in several of the above-referenced copendingpatent applications.

Another possibility of scattering of the light incident on the layer 42is represented by light ray or beam 54, which either is reflected by thereflector surface 43 or by total internal reflection occuring in theprotective layer 41 at the interface with the support 6 or other medium,as light ray 55 directed back to the liquid crystal layer 42 stillfurther enhancing or brightening the same. Some of the light scatteredby the liquid crystal layer 42 also may be transmitted out the left sideor right side of the layer relative to the illustration of FIG. 8; but arelatively small amount of such side-wise scattering will occur.

In FIG. 9 the liquid crystal material 30 in the containment medium 32 isin the isotropic phase. Therefore, the liquid crystal layer 42 issubstantially optically transparent. Accordingly, the incident light 44along light path 11 is transmitted substantially completely through thesegment 2, as is represented by the light 44' exiting the segment at theleft-hand side thereof. As a result, from the view direction 21 thesegment 2 will appear relatively dark or black, especially relative toother bright scattering segments.

Thus, it will be appreciated that the liquid crystal temperature sensor1 provides the ability to sense temperatures at relatively high levels.The invention also provides for high visibility to distinguish thedifference between the scattering/bright, specifically the enhancedbrightness, of that contained liquid crystal material which is in themesomorphic or anisotropic phase relative to that liquid crystal whichis in the isotropic phase. Reflection provided by total internalreflectance properties and the reflection occurring at the surface 43further enhances brightness of the liquid crystal material in themesomorphic phase. If desired, the surface 43 may be partly reflective,non-reflective or even optically absorbent, but scattering by themesomorphic liquid crystal still will occur and brightness still will beenhanced to the extent that total internal reflection still would beoccurring at the interface 45 and/or partial reflection occurs at thepartial reflector. The advantage of an absorbent surface 43 is theability thereof to absorb incident light further darkening theappearance of an isotropic liquid crystal material segment that is abovetransition temperature. A spacer (not shown) may be provided between theabsorbent surface 43 and the bottom of the liquid crystal layer 42 orprotective layer 41 to improve total internal reflection characteristicsas is described, for example, in several of the above-referencedapplications.

The invention preferably employs nematic liquid crystal material orsmectic liquid crystal material, both of which are capable ofcurvilinear alignment or distortion in the manner described above andboth of which in response to temperature generally exhibit a change inoptical characteristics other than direct color changes, the latterprimarily being the case with respect to cholesteric liquid crystalmaterial.

Preferably the liquid crystal materials employed have a good clearingpoint (transition temperature) both in terms of optical clarity (abovethe clearing point) and accuracy, narrowness or distinctiveness of theclearing point (i.e. the clearing point temperature accruately isdefined and that the same has been reached easily is observable).Exemplary liquid crystal materials which have these characteristics arethose of the hydroquinone group. It also has been found that liquidcrystal materials which are derivatives of the alkyl phenol esters areparticularly desirable because they have very narrow clearing pointsand, therefore, are very accurate for temperature measuring function.

Furthermore, preferred liquid crystal materials for the presentinvention are those which will mix well with each other to provide aclearing point that is a function of the respective clearing points andrelative amounts of the liquid crystal materials mixed. Not all liquidcrystal materials are mixable to form a good clearing point material.However, it has been found that liquid crystal materials that are estersand hydroquinones do mix well and do provide a good clearing point (i.e.accurately defined and readily distinguishable and observable).

As was mentioned above, liquid crystal materials useful in accordancewith the invention may be compositions which are derivatives ofhydroquinones, and more particularly, methyl hydroquinones. The liquidcrystal materials of this type can be represented by the followingformula ##STR1## wherein each R is independently a lower alkyl or loweralkoxy group, and R' is a lower alkyl group. In the context of thisinvention, lower alkyl or lower alkoxy group is intended to includegroups containing from about 1 to about 8 carbon atoms. Specificexamples of the R groups include methyl, ethyl, propyl, butyl, pentyl,octyl, methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, etc. R'preferably is a methyl group.

Exemplary radicals R and the isotropic transition temperature of aliquid crystal material including the same and wherein R¹ is methyl are

    ______________________________________                                        Radical       Transition Temp. (°C.)                                   ______________________________________                                        R = pentyl    140°                                                     R = butyloxy  206°                                                     R = hexyloxy  172°                                                     R = butyl     139°                                                     ______________________________________                                    

Specific examples of the hydroquinone-based liquid crystal materialsused in this invention including their transition temperature includethe following: bis-(4-butoxybenzoyl)-2-methyl hydroquinone (204° C.),bis-(4-pentylbenzoyl)-2-methyl hydroquinone (140° C.),bis-(4-pentoxybenzoyl)-2-methyl hydroquinone,bis-(4-hexoxybenzoyl)-2-methyl hydroquinone (172° C.),bis-(4-butylbenzoyl)-2-methyl hydroquinone,bis-(4-methoxybenzoyl)-2-methyl hydroquinone, etc. Mixtures of thesehydroquinone-based liquid crystal molecules may be utilized.

Other materials that could be added to a hydroquinone chain and used asliquid crystal material according to the invention include carboxylicesters, such as acetate, propionate, butyrate, hexanoate, etc., andcarboxy, such as methyl carboxy, ethyl carboxy, pentyl carboxy, etc.

Other exemplary liquid crystal materials useful according to theinvention include, for example, those listed in Table 1 below. Table 1also indicates which materials can readily be combined, and transitiontemperature of each material is indicated.

                  TABLE 1                                                         ______________________________________                                                                   Transition                                         Nematic Liquid Crystal Mixtures                                                                          Point (°C.)                                 ______________________________________                                        PePPeOB 4-n-pentylphenyl-4-n-pentoxybenzoate                                                                 55°                                             and                                                                   PePMeOB 4-n-pentylphenyl-4-n-methoxybenzoate                                                                 42°                                             or                                                                            4-n-pentylphenyl-4-n-methoxybenzoate                                                                 42°                                             and                                                                           4-n-butylphenyl-4-n-heptylbenzoate                                                                   15°                                             or                                                                            4-n-hexyloxyphenyl-4-n-butylbenzoate                                                                 50°                                             and                                                                           4-n-heptoxyphenyl-4-n-butylbenzoate                                                                  43°                                             or                                                                            4-n-ethoxybenzyl-4-n-butylaniline                                                                    75.6°                                           and                                                                           4-n-butoxybenzyl-4-n-butylaniline                                                                    72.1°                                   ______________________________________                                         (an example of a smectic liquid crystal material)                        

An important advantage of the invention is that using the 15° C. liquidcrystal material of Table 1, for example, a composition, including suchliquid crystal material and one or more others, having a transitiontemperature that is below ordinary room ambient temperature of, say,about 18° C. to about 25° C. is possible and can be used in a liquidcrystal temperature sensor according to the invention.

The liquid crystal segments 2-5 may be dyed, if desired. If dyed thesegments may be dyed the same or different respective colors usingpreferably non-pleochroic dye(s). Exemplary dyes may be ordinary foodcoloring dyes. The dye preferably is mixed with the containment mediumor the dye may be applied by imbibition using one of the processesdescribed in the above-referenced application Ser. No. 480,461.Preferably the dye is a water soluble dye capable of dissolving in theor a component of the containment medium without affecting or dissolvingin the liquid crystal. Examples of such a dyed volume 29'" of liquidcrystal material according to the invention is illustrated in FIG. 10,where dye 60 is shown in the containment medium 32. An advantage of theenhanced brightness of the mesomorphic liquid crystal scattering lightis that since the light on average makes several passes through theencapsulated or contained liquid crystal material, a relatively smallamount of dye will still effect a substantial coloring of the lightscattered out from the liquid crystal segment to the viewing direction21. Desirably the dye is a high visibility dye, e.g. of green or magentacolor, for maximizing brightness. Ordinarily a dyed segment of isotropicphase liquid crystal material would be darker and less colored,preferably nearly uncolored in appearance, relative to a scatteringsegment.

One example of a preferred liquid crystal material useful in accordancewith the invention hereof is a liquid crystal that is a derivative ofmethyl hydroquinone.

EXAMPLE 1

A mixture of 32.5% (mole percent) ofbis(4-butoxybenzoyl)-2-methylhydroquinone and 67.6% ofbis(pentylbenzoyl)-2-methylhydroquinone was formed. (In Examples 2-5below, the compounds will be referred to as materials A and B,respectively. Both are or have properties of nematic liquid crystal.)About 10 ml chloroform (used as a solvent) was placed in a beaker, andabout 41/2 grams of such mixture was dissolved in the chloroform. About20 grams of 17% by weight solution polyvinyl alcohol (20/30 PVA byMonsanto, the remaining 83% by weight of the PVA solution was water) wasplaced in a beaker, and while stirring the same with a dremel (highspeed mixer that produces high shear), the chloroform and liquid crystalmixture was added slowly. After such addition, the mixture was dremeledfor a few additional minutes. The resulting mixture of encapsulatedliquid crystal material has a shelf life of months. As an alternative, asmall blender instead of a dremel could also be used to carry out suchencapsulation.

To the above "original" mixture, a 15% by weight solution of GantrezAN-169 (by GAF, the remaining 85% by weight of the Gantrez solutionbeing water) was added and stirred. The original mixture was 60% byweight of the final mixture, and the Gantrez solution was 40% by weightof the final mixture. The final mixture has a shelf life of only a fewdays. (Therefore, desirably the Gantrez AN-169 ordinarily would be addedjust prior to use/application of the encapsulated liquid crystalmixture).

One or more thin layer(s) of the final mixture was (were) coated on analuminum or nickel reflecting support surface and allowed to air drybetween each coating. The resulting material was like one of thesegments 2-5 described above in form and function; the same had atransition temperature of about 163° C.

Pure material A has a transition temperature or clearing point at about204° C. and a melting point of 113° C.; and pure material B has atransition temperature or clearing point at about 140° C. and a meltingpoint of about 64° C.

EXAMPLE 2

The method and materials of Example 1 were employed except that a 20% byweight solution of Gantrez AN-169 (the remaining 80% by weight of suchsolution being water) was substituted for the 15% Gantrez AN-169 ofExample 1. The results of the product formed and operation thereof weresubstantially the same as in Example 1.

EXAMPLE 3

The method of Example 1 was followed except that material A was 54.4% ofthe liquid crystal mixture and material B was 45.6% of the liquidcrystal mixture. Such mixture showed a transition temperature orclearing point of about 177° C.

EXAMPLE 4

The method of Example 1 was followed except that material A was 77.0% ofthe liquid crystal mixture and material B was 23.0% of the liquidcrystal mixture. Such mixture showed a transition temperature orclearing point of about 191° C.

EXAMPLE 5

The method of Example 1 was followed except that material A was 100.0%of the liquid crystal mixture and no material B was used. Such materialshowed a transition temperature or clearing point of about 204° C.

The foregoing presents several examples of high temperature liquidcrystal materials and mixtures thereof that may be used as the liquidcrystal composition in the liquid crystal temperature sensor of theinvention. It will be appreciated that such materials may be used atdifferent respective segments 2-5 of the device 1 (FIGS. 1-3) to providean indication of whether the temperature sensed by the invention exceedsany one or more of the clearing points or transition temperatures ofsuch mixtures. The mixtures of Examples 1-5 did not experience anycrystallization problems.

Several characteristics of the containment medium are noted. Forexample, it is desirable that the containment medium be waterresistant--such medium should not dissolve in water. The liquid crystalmaterial and components therein should not be soluble in the containmentmedium. Furthermore, for high temperature uses, say above 100° C., thecontainment medium should be temperature resistant, for example, isoptically and otherwise stable; particularly such medium should notbrown or otherwise discolor or at least should only discolor relativelyslowly in response to relatively high temperatures and should remainsubstantially optically transparent.

Examples of containment or encapsulating medium materials that may beemployed in accordance with the present invention, such as polyvinylalcohol (hereinafter sometimes referred to as PVA), Gantrez (usedinterchangeably herein to refer to polymaleic products, in particular toa poly(methylvinylether/maleic anhydride) which is sold by GAF, and toequivalent materials--where Gantrez is referred to herein it is to beunderstood that equivalent materials may be employed in place thereof),gelatin, Carbopoie (a carboxy polymethylene polymer of B.F. GoodrichChemical Corporation--where Carbopole is referred to herein it is to beunderstood that equivalent materials may be employed in place thereof),other polymers, etc., are presented in the above referenced patent andapplications which deal with encapsulated or contained distorted andcurvilinearly aligned liquid crystal, and the same are incorporated byreference in their entireties. Examples and characteristics of severalPVA materials useful in the invention are shown in Table 2, as follows:

                                      TABLE 2                                     __________________________________________________________________________                                               TEMPERATURE                        CONTAINMENT MEDIUM                         &                                  (PVA)          VISCOSITY                                                                            % HYDROLYZED                                                                            MOLECULAR Wgt.                                                                           % SOLUTIONS                        __________________________________________________________________________    20-30          4-6 CPS                                                                              88.7-85.5 10,000     4% at 20° C.                Galvatol, by                                                                  Monsanto Company                                                              40-20          2.4-3 CPS                                                                            77-72.9    3,000     4% at 20° C.                Galvatol, by                                                                  Monsanto Company                                                              523            21-25  87-89     --         4% at 20° C.                Air Products and                                                              Chemicals, Inc.                                                               72-60          55-60  99-100    --         4% at 20° C.                Elvanol, by                                                                   DuPont Company                                                                405            2-4 CPS                                                                              80-82     --         4% at 20° C.                Poval, by                                                                     Kurashiki                                                                     __________________________________________________________________________

Although some of the aforesaid materials may be used alone or in variousmixtures and combinations, some of such materials may encounter browningat elevated temperature and (especially polymers) also may tend todissolve the liquid crystal at elevated temperatures.

It has been discovered that the inclusion of Gantrez or Carbopole in thecontainment medium helps to improve the water resistance of theencapsulated or contained liquid crystal material as a whole. This isparticularly true for containment media formed of mixtures of PVA andGantrez and mixtures of PVA and Carbopole; and Gantrez and the Carbopolematerials or types of materials prevent water solubility of the PVA.Gantrez is sold by GAF and generically may be identified aspoly(methylvinylether/maleic anhydride). A preferred Gantrez product isthat sold by GAF as Gantrez AN-169. Other Gantrez products that wouldwork in the invention are those identified as Gantrez AN-119, -139, and-149; but Gantrez AN-169 is preferred. Other equivalent functioningpolymaleic products also may be substituted for Gantrez. Equivalentproducts also may be substituted for the Carbopole material.

Preferred containment medium for the liquid crystal in accordance withthe invention, especially for relatively high temperature liquid crystalsensors, is a combination of polyvinyl alcohol and Gantrez. Thepolyvinyl alcohol is water soluble and can readily be mixed with watersoluble dye to provide a coloring of the containment medium. The watersoluble polyvinyl alcohol also conveniently can be used to encapsulatean oil base or oil soluble liquid crystal material to form the desiredvolumes of liquid crystal, e.g. by mixing the PVA and liquid crystal toform an emulsion or an emulsion-like consistency material of PVA andliquid crystal. The addition of Gantrez to such emulsion would result ina reaction between the PVA and Gantrez to form a polyester. Thepolymaleic product, such as Gantrez, or equivalently used material,should be water soluble so it will mix will and react well with the PVA.Polyester is insoluble in water and results in a final containmentmedium that is quite stable when allowed to set up as, for example, anencapsulated liquid crystal layer 42 in a segment 2-5.

Gantrez, more particularly, poly(methylvinylether/maleic anhydride), maybe used alone as a containment medium, i.e. without being combined withPVA. However, properties, e.g. with respect to water resistance andoptical stability at high temperature, would not be as desirable asthose properties would be using a combination of Gantrez and PVA.

It has been found that such containment medium of resulting polyester orin any event of polyvinyl alcohol and poly(methylvinylether/maleicanhydride), preferably Gantrez, has relatively stable opticalcharacteristics, including particularly the ability even when subjectedto relatively high temperatures not to discolor or to brown or at leastonly to undergo relatively slow discoloring or browning, especially whencompared to the relatively rapid discoloring of other containment media.The liquid crystal material also does not tend to discolor or todissolve in the resulting polyester containment medium of the invention.

The preferred PVA is that identified as 20/30, which is an indication ofthe viscosity. Other PVA materials also may be used. Such materialsshould have suitable viscosity to achieve desired lay down (e.g. onsupport 6 while in emulsion with liquid crystal material) levelling, andlike characteristics that may be a function of viscosity and viscositycontrol.

Any ratio of PVA and Gantrez (or other equivalent polymaleic product)may be used to form the containment medium. However, preferably thecontainment medium should be formed of, for example, from about 5% toabout 80% Gantrez (or equivalently functioning polymaleic product) andfrom about 95% to about 20% PVA. Most preferred would be a ratio that isabout mid-range of the noted preferred ratios. According to thepreferred embodiment and best mode of the present invention, then, thebest non-browning containment medium is formed of PVA and Gantrez in theratio ranges just mentioned above.

As was mentioned above, the liquid crystal material should not besoluble, indeed it should not have partial solubility, in thecontainment medium, whether the latter is PVA, Gantrez, other material,or mixture(s) thereof. Thus, all components of the liquid crystalmaterial should stay in the liquid crystal material and should notdissolve in the containment medium.

The solvent mentioned in Examples 1-5 above was chloroform. Othersolvents also may be used; examples include dimethylglycol ether anddiethylglycol ether.

According to the invention various transition temperatures can beachieved for liquid crystal material compositions by mixing pluralliquid crystal materials that have different respective transitiontemperature characteristics. The resulting composition will have atransition temperature that is a function of or related to thetransition temperature of each ingredient and the relative amounts ofeach ingredient in the composition. Indeed, as is shown in FIG. 11, thetransition temperature of a mixture of liquid crystal materials havingdifferent transition temperatures will vary generally linearly withrespect to the relative amounts in mole percent of the liquid crystalmaterials used in the liquid crystal mixture or composition. The slopeof each curve in FIG. 11 will be a function of the transitiontemperature of each ingredient in the composition.

EXAMPLE 6

A number of mixtures of liquid crystal material(s) with encapsulating orcontainment medium were made and the clearing point or transitiontemperature for each were measured. The results of such measurementswere graphed, as is shown in FIG. 11. Curve 100 in FIG. 11 representsvarious mole percent (mixture) of liquid crystal mixture(s) C and/or D;curve 101 represents various mole percent of liquid crystal mixture(s) Cand/or E; and curve 102 represents various mole percent of liquidcrystal mixture(s) D and/or E. Mixes C, D, and E are defined below.Thus, at the lower left-hand end of curve 100, the liquid crystalmixture made and tested for clearing point consisted substantiallyexclusively of liquid crystal mixture C; and at the upper right-hand endof curve 100 the liquid crystal made and tested for clearing pointconsisted substantially exclusively of liquid crystal mixture D. At thevarious mid-portions of curve 100 are represented combinations of liquidcrystal mixtures C and D in the approximate mole percents represented onthe vertical axis of the graph of FIG. 11; and the clearing point ofsuch material can be read along the horizontal axis at the bottom of thegraph.

For Example 6, the encapsulation material or containment medium wasformed of 22% by weight (the rest was water) of 20/30 polyvinyl alcoholwith a 0.1% surfactant of LD-630 (by GAF) and a selected amount of dye.Also, a 20% by weight solution of Gantrez was mixed with the mixture oremulsion of liquid crystal material and encapsulation material as isdescribed herein.

The dye was geen food color from McCormick. Different concentrations ofdye were tested empirically until a good contrast before and afterclearing was achieved. The amount of dye empirically determined wasapproximately 1 ml of dye in 250 ml of polyvinyl alcohol solution.Different amounts and/or colors of dye may be used for each encapsulatedliquid crystal material element (shown as elements 2-5 in FIG. 1, forexample) used to indicate different respective temperatures, thusfacilitating visual temperature discrimination by a person using aliquid crystal temperature sensor 1 according to the invention.

The purpose of the surfactant used in Example 6 is to provide bettercoating properties of the encapsulated liquid crystal material, i.e. tofacilitate applying the same in a generally uniform manner to a surface,such as the surface of the support 6 (FIG. 1). Uniformity may be ofthickness and/or other characteristics of the encapsulated liquidcrystal layer comprised of the liquid crystal material and containmentmedium. Surfactants, including the exemplary LD-630 and/or others, notsoluble in the liquid crystal material itself or which arepreferentially held in the containment medium may be used according tothis aspect of the invention.

The liquid crystal material used, namely those identified above asmixtures C, D, and E were, as follows:

    ______________________________________                                        Mix C)                                                                              PPMeOB-                    39.6%,                                             PPPOB-                     26.6%                                              Ethylphenyl-propylbenzoate-                                                                              33.8%                                        Mix D)                                                                              PPMeOB-                    60%                                                PPPOB-                     40%                                          Mix E)                                                                              A mixture of about 52% of                                                     (1) A mix of PPMeOB 60% and PPPOB 40%-                                                                   82%                                                (2) bis(4-butoxybenzoyl)-2-methylhydroquinone-                                                           18%                                                and about 48% of                                                              (1) CnPPeB-                33%                                                (2) CnPHepB-               50%                                                (3) bis(pentylbenzoyl)-2-methylhydroquinone-                                                             16.6%                                        ______________________________________                                    

The liquid crystal temperature sensor also would work without the dyementioned in this Example 6. However, if dye is used, as is described inthis Example 6, then the dye should be water soluble which dissolves inthe containment medium but will not dissolve in the liquid crystalmaterial and cause a shift in the temperature, etc. characteristics ofthe liquid crystal material. The dye also should be a relatively highvisibility dye, such as green or magenta to maximize the visibility ofthe liquid crystal segments of the liquid crystal temperature sensor ofthe invention.

According to the method of encapsulation of the liquid crystalmaterial(s) selected from one or two of the above Mixes C, D, and E, 15grams of polyvinyl alcohol 20/30, 22% solution (the other 78% beingwater), with dye was placed in a 50 ml beaker, and the ingredients werestirred with a dremel at medium speed. While the stirring continued, 5grams of filtered liquid crystal material the selected liquid crystalMix or Mixes was (were) added dropwise. The mixture was stirred for anadditional 1/2 minute after such addition of liquid crystal materialproducing an emulsion. To the final emulsion was added a solution of 20%Gantrez.

A slide was prepared and checked under a microscope for unencapsulatedliquid crystal material. The ideal mixture was determined to haverelatively large capsule sizes with total encapsulation, i.e. all theliquid crystal material encapsulated. The clearing temperature of eachsample was checked after the slide was completely dry, and the resultsare presented on the graph of FIG. 11.

As is seen in the graph of FIG. 11, the clearing or transitiontemperatures of the materials used in Example 6 ranged from about 25° C.to about 70° C. Such temperature range is lower than that of thematerials used to sense higher temperatures, e.g. presented in Examples1-5, and, therefore, the need for Gantrez in the containment medium ofthe lower temperature compositions to prevent browning, etc., ordinarilywould be unnecessary, as long as a device using such lower temperaturesordinarily would not be subjected to the relatively higher temperatures.PVA or equivalent material that prevents contamination of the liquidcrystal material preferably should be used in both the relatively lowerand higher temperature sensor embodiments disclosed herein.

STATEMENT OF INDUSTRIAL APPLICATION

With the foregoing in mind, it will be appreciated that the variousliquid crystal materials contained in volumes in a containment mediummay be placed on a support and used to sense temperature and to provideoutput information of the sensed temperature.

I claim:
 1. A temperature sensor and indicator, comprisingliquid crystalmeans for scattering or transmitting light incident thereon as afunction of temperature of said liquid crystal means, containment meansfor containing plural volumes of said liquid crystal means, saidcontainment means comprising means for distorting the natural structureof said liquid crystal means to distorted, curvilinearly alignedstructure, and support means for supporting said volumes of liquidcrystal means in said containment means for sensing temperature, saidliquid crystal means having a mesomorphic or anisotopic phase attemperatures below a transition temperature and an isotropic phase attemperatures at and above such transition temperature, furthercomprising light source means for illuminating said liquid crystal meansin said containment means, said light source means being positioned withrespect to said liquid crystal means and containment means to directincident light thereon generally along a path out of the expectedviewing direction of said liquid crystal means, said containment meanscomprising means for containing said liquid crystal material incurvilinear alignment configuration at least at temperatures below suchtransition temperature, and said liquid crystal material, when in suchmesomorphic or anisotropic phase, having an index of refractiondifferent from said containment means to scatter light incident thereonand said liquid crystal material, when in such isotropic phase, havingan index of refraction substantially matched to that of said containmentmeans to reduce such scattering of light incident thereon whereby thatliquid crystal means below such transition temperature scatters lightfrom said light source toward such viewing direction causing such liquidcrystal means to appear relatively bright and above such transitiontemperature such liquid crystal means reduces such scattering andappears relatively dark.
 2. A temperature sensor and indicator,comprisingliquid crystal means for scattering or transmitting lightincident thereon as a function of temperature of said liquid crystalmeans, containment means for containing plural volumes of said liquidcrystal means, said containment means comprising means for distortingthe natural structure of said liquid crystal means to distorted,curvilinearly aligned structure, and support means for supporting saidvolumes of liquid crystal means in said containment means for sensingtemperature, said liquid crystal means having a mesomorphic oranisotropic phase at temperatures below a transition temperature and anisotropic phase at temperatures at and above such transitiontemperature, said liquid crystal means comprising a composition ofmatter, (percentages refer to mole percent) includinga. from about 30%to less than about 100% bis(4-butoxylbenzoyl)-2-methylhydroquinone, andb. from more than about 0% to about 70%bis(4-pentylbenzoyl)-2-methylhydroquinone.
 3. The invention of claim 2,said liquid crystal means having a transition temperature from about140° C. to about 205° C.
 4. A temperature sensor and indicator,comprisingliquid crystal means for scattering or transmitting lightincident thereon as a function of temperature of said liquid crystalmeans, containment means for containing plural volumes of said liquidcrystal means, said containment means comprising means for distortingthe natural structure of said liquid crystal means to distorted,curvilinearly aligned structure, and support means for supporting saidvolumes of liquid crystal means in said containment means for sensingtemperature, said liquid crystal means having a mesomorphic oranisotropic phase at temperatures below a transition temperature and anisotropic phase at temperatures at and above such transitiontemperature, said containment means comprising means for containing saidliquid crystal material in curvilinear alignment configuration at leastat temperatures below such transition temperature, and said liquidcrystal material, when in such mesomorphic or anisotropic phase, havingan index of refraction different from said containment means to scatterlight incident thereon and said liquid crystal material, when in suchisotropic phase, having an index of refraction substantially matched tothat of said containment means to reduce such scattering of lightincident thereon.
 5. The invention of claim 4, said containment meanscomprising a material that undergoes slow or no discoloring in responseto relatively high temperature and that does not dissolve said liquidcrystal means at relatively high temperature.
 6. The invention of claim5, said containment means comprising a mixture of at least one polyvinylalcohol and at least one poly(methylvinyl ether/maleic anhydride). 7.The invention of claim 4, further comprising dye means for coloringlight scattered by said liquid crystal means.
 8. The invention of claim7, said dye comprising a high visibility water soluble dye in saidcontainment means, said dye being insoluble in said liquid crystalmeans.
 9. The invention of claim 4, said liquid crystal means comprisingnematic or smectic liquid crystal.
 10. The invention of claim 4, saidliquid crystal means comprising operationally nematic or operationallysmectic liquid crystal.
 11. The invention of claim 4, said liquidcrystal means comprising a material selected from the group comprisingat least smectic liquid crystal and nematic liquid crystal, saidmaterial being in the absence of a cholesteric liquid crystal materialadmixed therewith.
 12. A temperature sensor, comprisingliquid crystalmaterial having an isotropic phase at and above a transition temperatureand a mesomorphic or anisotropic phase below such transitiontemperature, containment means for containing said liquid crystalmaterial in curvilinear alignment configuration at least at temperaturesbelow such transition temperature, and said liquid crystal material,when in such mesomorphic or anisotropic phase, having an index ofrefraction different from said containment means to scatter lightincident thereon and said liquid crystal material, when in suchisotropic phase, having an index of refraction substantially matched tothat of said containment means to reduce such scattering of lightincident thereon.
 13. The invention of claim 12, said liquid crystalmaterial comprising a material selected from the group comprising atleast smectic liquid crystal and nematic liquid crystal, said materialbeing in the absence of a cholesteric liquid crystal material admixedtherewith.
 14. The invention of claim 12, said liquid crystal materialcomprising a composition of matter, includinga) from 0 to 100 molepercent of a first liquid crystal material, and b) from 0 to 100 molepercent of a second liquid crystal material,such that the total of theliquid crystal materials equals 100 mole percent, said composition ofmatter having a mesomorphic or anisotropic phase at temperatures below atransition temperature and an isotropic phase at and above suchtransition temperature, and said transition temperature being in therange of about 15° C. to about 205° C.
 15. A temperature sensor,comprising liquid crystal means for scattering or transmitting lightincident thereon as a function of temperature of said liquid crystalmeans, and containment means for containing plural volumes of saidliquid crystal means, said containment means comprising a material thatundergoes no or slow discoloring in response to relatively hightemperature and that does not dissolve said liquid crystal means atrelatively high temperatures,said containment means comprising a mixtureof at least one polyvinyl alcohol and at least one poly(methylvinylether/maleic anhydride), said mixture comprising from about 5% to about80% of the poly(methylvinyl ether/maleic anhydride).
 16. The inventionof claim 15, said mixture comprising 20/30 polyvinyl alcohol.
 17. Atemperature sensor, comprising liquid crystal means for scattering ortransmitting light incident thereon as a function of temperature of saidliquid crystal means, and containment means for containing pluralvolumes of said liquid crystal means, said containment means comprisinga material that undergoes no or slow discoloring in response torelatively high temperature and that does not dissolve said liquidcrystal means at relatively high temperatures, comprisingliquid crystalmeans having an isotropic phase at and above a transition temperatureand a mesomorphic or anisotropic phase below such transitiontemperature, containment means for containing said liquid crystal meansin curvilinear alignment configuration at least at temperatures belowsuch transition temperature, and said liquid crystal means, when in suchmesomorphic or anisotropic phase, having an index of refractiondifferent from said containment means to scatter light incident thereonand said liquid crystal means, when in such isotropic phase, having anindex of refraction substantially matched to that of said containmentmeans to reduce such scattering of light incident thereon.
 18. Theinvention of claim 17, wherein said liquid crystal means has atransition temperature of a magnitude that is below room ambienttemperature.
 19. The invention of claim 17, wherein said liquid crystalmeans has a transition temperature of from about 15° C. to about 400° C.20. A temperature sensor, comprising liquid crystal means for scatteringor transmitting light incident thereon as a function of temperature ofsaid liquid crystal means, and containment means for containing pluralvolumes of said liquid crystal means, said liquid crystal meanscomprising at least one of nematic liquid crystal material and smecticliquid crystal material in the absence of a cholesteric liquid crystalmaterial admixed therewith,said liquid crystal means comprising amixture of at least two liquid crystal material ingredients, one of saidliquid crystal material ingredients having a relatively high transitiontemperature and the other having a relatively lower transitiontemperature, the transition temperature of said mixture of said liquidcrystal materials being a function of the properties of each of saidliquid crystal material ingredients in said mixture, wherein liquidcrystal means has a transition temperature of a magnitude that is belowroom ambient temperature, and wherein said liquid crystal means has atransition temperature of from about 15° C. to about 400° C.
 21. Atemperature sensor and indicator, comprisingliquid crystal means forscattering or transmitting light incident thereon as a function oftemperature of said liquid crystal means, containment means forcontaining plural volumes of said liquid crystal means, said containmentmeans comprising means for distorting the natural structure of saidliquid crystal means to distorted, curvilinearly aligned structure, andsupport means for supporting said volumes of liquid crystal means insaid containment means for sensing temperature, said liquid crystalmeans having a mesomorphic or anisotropic phase at temperatures below atransition temperature and an isotropic phase at temperatures at andabove such transition temperature, said containment means beinginsoluble in water, said containment means being formed of a reaction ofone water soluble material and another material.
 22. The invention ofclaim 21, said containment means comprising a polyester.
 23. Atemperature sensor, comprising liquid crystal means for scattering ortransmitting light incident thereon as a function of temperature of saidliquid crystal means, and containment means for containing pluralvolumes of said liquid crystal means, said liquid crystal meanscomprising at least one of operationally nematic liquid crystal materialand operationally smectic liquid crystal material in the absence of acholesteric liquid crystal material admixed therewith.
 24. The inventionof claim 23, said liquid crystal means having a mesomorphic oranisotropic phase at temperatures below a transition temperature and anisotropic phase at temperatures at and above such transitiontemperature.
 25. The invention of claim 23, said containment meanscomprising a material that undergoes no or slow discoloring in responseto relatively high temperature and that does not dissolve said liquidcrystal means at relatively high temperature.
 26. A liquid crystaldevice, comprising liquid crystal means for scattering or transmittinglight incident thereon as a function of a prescribed input, containmentmeans for containing said liquid crystal means in curvilinear alignmentconfiguration, and said liquid crystal means being operationallysmectic, having a mesomorphic or anisotropic phase, and having index ofrefraction characteristics for selectively transmitting or scatteringlight.
 27. The invention of claim 26, said containment means forcontaining plural volumes of said liquid crystal means, said containmentmeans comprising a material that undergoes no or slow discoloring inresponse to relatively high temperature and that does not dissolve saidliquid crystal means at relatively high temperature.
 28. The inventionof claim 27, said liquid crystal means comprising operationally nematicor operationally smectic liquid crystal material.
 29. The invention ofclaim 27, said liquid crystal means comprising a mixture of at least twoliquid crystal materials, each of said liquid crystal materials beingoperationally nematic or operationally smectic, and each having amesomorphic or anisotropic phase at temperatures below a respectivetransition temperature and an isotropic phase at temperatures at andabove such respective transition temperature, said mixture having atransition temperature characteristic that is a function of therespective transition temperatures of said at least two liquid crystalmaterials and the quantity of each in the mixture, and said mixturehaving a mesomorphic or anisotropic phase at temperatures below atransition temperature thereof and an isotropic phase at temperatures atand above such transition temperature thereof.
 30. A liquid crystaltemperature sensor, comprising a mixture of at least two liquid crystalmaterials, each of said liquid crystal materials being operationallynematic or operationally smectic, and each having a mesomorphic oranisotropic phase at temperatures below a respective transitiontemperature and an isotropic phase at temperatures at and above suchrespective transition temperature, said mixture having a transitiontemperature characteristic that is a function of the respectivetransition temperatures of said at least two liquid crystal materialsand the quantity of each in the mixture, and said mixture having amesomorphic or anisotropic phase at temperatures below a transitiontemperature thereof and an isotropic phase at temperatures at and abovesuch transition temperature thereof.
 31. The invention of claim 30, saidliquid crystal material being in the absence of cholesteric liquidcrystal material admixed therewith.
 32. The invention of claim 30, saidcontainment means comprising containment means for containing pluralvolumes of said liquid crystal means and means for distorting thenatural structure of said liquid crystal means to distorted,curvilinearly aligned structure at temperatures below the transitiontemperature of said liquid crystal means.
 33. The invention of claim 30,said liquid crystal material, when in mesomorphic or anisotropic phase,having an index of refraction different from said containment means toscatter light incident thereon and said liquid crystal material, when inisotropic phase, having an index of refraction substantially matched tothat of said containment means to reduce such scattering of lightincident thereon.
 34. The invention of claim 30, further comprisingsupport means for supporting said liquid crystal means in saidcontainment means for sensing temperature.
 35. The invention of claim30, further comprising reflecting means for reflecting light scatteredby said liquid crystal means.
 36. The invention of claim 30, furthercomprising light source means for illuminating said liquid crystal meansin said containment means, said light source means being positioned withrespect to said liquid crystal means and containment means to directincident light thereon generally along a path out of the expectedviewing direction of said liquid crystal means.
 37. The invention ofclaim 30, said liquid crystal means comprising plural segments of liquidcrystal means in containment means, a plurality of said segments havingdifferent respective transition temperatures.
 38. The invention of claim30, said containment means comprising a mixture of at least onepolyvinyl alcohol and at least one poly(methylvinyl ether/maleicanhydride).
 39. The invention of claim 38, said mixture comprising fromabout 5% to about 80% of the poly(methylvinyl ether/maleic anhydride).40. The invention of claim 38, wherein said mixture further comprises asolvent.
 41. The invention of claim 40, said solvent comprising at leastone selected from the group comprising chloroform, dimethylglcol ether,and diethylglycol ether.
 42. The invention of claim 30, wherein saidcontainment means is insoluble in water.
 43. The invention of claim 30,wherein said containment means comprises a polyester.
 44. The inventionof claim 30, wherein said containment means comprises a combination ofat least two materials, at least one of said materials ordinarily beingwater soluble, and at least another of said materials being reactivewith said one material to make said containment means water insoluble.45. The invention of claim 30, said liquid crystal means comprising acomposition of matter, including (a) from more than about 0 to less thanabout 100 mole percent of a first liquid crystal material, and (b) frommore than about 0 to less than about 100 mole percent of a second liquidcrystal material, said composition of matter having a mesomorphic oranisotropic phase at temperatures below a transition temperature and anisotropic phase at and above such transition temperature, and suchtransition temperature of the composition being a function of thetransition temperature of each of said liquid crystal materials and therelative amounts of each liquid material in the composition.
 46. Theinvention of claim 45, wherein said transition temperature of saidcomposition is in the range of from about 15° C. to about 400° C. 47.The invention of claim 46, wherein each of said first and second liquidcrystal materials is selected from a respective one of the followingcompositions, (percentages refer to mole percent): Mix A, PPMeOB 39.6%,PPPOB 26.6% and Ethylphenylpropylbenzoate 33.8%; Mix B, PPMeOB 60% andPPPOB 40%; and Mix C, a mixture of about 52% of (1) a mix of PPMeOB 60%and PPOB 40% 82% and (2) bix(4-butoxybenzoyl)-2-methylhydroquinone 18%and about 48% of (1) CnPPeB 33%, (2) CnPHepB 50%, and (3)bix(4-pentylbenzoyl)-2-methylhydroquinone 16.6%.
 48. The invention ofclaim 30, said liquid crystal means comprising a composition of matter,(percentages refer to mole percent) including (a) from about 30% to lessthan about 100% bis(4-butoxylbenzoyl)-2-methylhydroquinone, and (b) fromabout more than 0% to about 70%bix(4-pentylbenzoyl)-2-methylhydroquinone.
 49. The invention of claim48, said liquid crystal means having a transition temperature from about140° C. to about 205° C.
 50. The invention of claim 30, wherein saidliquid crystal means has a transition temperature of a magnitude that isbelow room ambient temperature.
 51. The invention of claim 30, furthercomprising dye means for coloring light scattered by said liquid crystalmeans.